Segment Information (Information About Industry Segments And Geographic Areas) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,566,711,000	$ 1,605,315,000	$ 4,710,169,000	$ 4,684,248,000
Total revenues	1,566,711,000	1,605,315,000	4,710,169,000	4,684,248,000
Operating income (loss)	73,597,000	58,044,000	215,380,000	164,444,000
Restructuring expenses	(398,000)	(601,000)	(799,000)	(652,000)
Gain on sale of building	11,749,000	0	11,749,000	0
Interest expense	(2,397,000)	(2,351,000)	(6,887,000)	(5,978,000)
Interest income	186,000	234,000	641,000	862,000
Income from continuing operations before income taxes	71,386,000	55,927,000	209,134,000	159,328,000
Total assets	3,434,667,000		3,434,667,000		3,465,915,000
Insurance recoveries				2,600,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(17,766,000)	(34,169,000)	(60,633,000)	(90,923,000)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(18,481,000)	(19,532,000)	(50,192,000)	(50,953,000)
Restructuring expenses			(300,000)	0
Total assets	451,903,000		451,903,000		482,388,000
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,479,909,000	1,525,588,000	4,450,481,000	4,422,676,000
Total revenues	1,479,909,000	1,525,588,000	4,450,481,000	4,422,676,000
Operating income (loss)	77,645,000	74,985,000	241,975,000	204,204,000
Total assets	2,847,036,000		2,847,036,000		2,822,699,000
UNITED STATES | United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	314,666,000	340,529,000	958,295,000	984,443,000
UNITED STATES | United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	565,227,000	616,403,000	1,616,794,000	1,741,483,000
UNITED STATES | United States Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	427,564,000	457,777,000	1,293,750,000	1,361,392,000
UNITED STATES | United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	172,452,000	110,879,000	581,642,000	335,358,000
UNITED STATES | Operating Segments [Member] | United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	316,409,000	347,488,000	971,361,000	1,000,598,000
Operating income (loss)	20,666,000	23,971,000	67,162,000	68,147,000
Restructuring expenses			(375,000)	0
Total assets	333,416,000		333,416,000		329,742,000
UNITED STATES | Operating Segments [Member] | United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	569,794,000	629,481,000	1,632,511,000	1,780,112,000
Operating income (loss)	30,206,000	27,421,000	78,052,000	56,809,000
Restructuring expenses			(124,000)	(473,000)
Total assets	805,382,000		805,382,000		795,256,000
UNITED STATES | Operating Segments [Member] | United States Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	438,864,000	471,576,000	1,324,816,000	1,395,607,000
Operating income (loss)	19,388,000	23,285,000	53,606,000	52,928,000
Restructuring expenses			0	(179,000)
Total assets	749,382,000		749,382,000		756,785,000
UNITED STATES | Operating Segments [Member] | United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Total revenues	172,608,000	111,212,000	582,426,000	337,282,000
Operating income (loss)	7,385,000	308,000	43,155,000	26,320,000
Total assets	958,856,000		958,856,000		940,916,000
UNITED KINGDOM | United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	86,802,000	79,727,000	259,688,000	261,572,000
UNITED KINGDOM | Operating Segments [Member] | United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	86,802,000	79,727,000	259,688,000	261,572,000
Operating income (loss)	3,082,000	3,192,000	12,647,000	11,845,000
Total assets	135,728,000		135,728,000		160,828,000
United Kingdom Subsidiary [Member]
Segment Reporting Information [Line Items]
Income from reduction in estimate of certain accrued contract costs	$ 0		$ 4,800,000